This invention relates to solid state circuit interrupters employing digital electronic trip units. One such solid state circuit interrupter is described within U.S. Pat. No. 4,589,052, which Patent is incorporated herein for purposes of reference. Such electronic trip units are used in circuit interrupters and are capable of acting on a number of programmed setpoint trip parameters to interrupt the circuit being protected in a timely manner. One such electronic trip unit which allows for user interaction and which provides capability both to select trip parameters and to view the selected trip parameters is found within U.S. Pat. No. 4,672,501, which Patent is also incorporated herein for purposes of reference.
For purposes of reducing cost while maintaining accuracy and functionality of the electronic trip units, microprocessors are being employed to gather information, process the information, and provide a means of monitoring the information using associated digital circuitry. The use of such microprocessors allows more protection functions to be contained in smaller-sized packages. Smaller-sized circuit interrupters because of limited space requirements do not contain the means required to enter data or to view the data being processed. The user-interfaces employed on larger-sized molded case circuit interrupters typically consist of rotatable switches with associated printed indicia to indicate the relative switch positions. The amount of area available on the front panel of such circuit interrupters is also limited and hence reduces the number of optional features requiring such switches.
A separate portable display and keypad in the form of a self-contained unit, powered by an internal power supply, which contains a microprocessor and associated circuitry and which communicates with the circuit interrupter trip unit using an infrared transmitter is described within U.S. Pat. No. 4,751,605. This arrangement requires a separate microprocessor and related digital circuitry within the portable display and keypad which adds to the overall cost of the circuit interrupter.
U.S. Pat. No. 4,814,712 describes a separate portable display and keyboard unit that is capable of reading stored setpoints within an associated circuit interrupter but is incapable of changing the setpoint parameters.
U.S. Pat. No. 4,870,531 entitled "Circuit Breaker with Removable Display and Keypad", which Patent is incorporated herein for reference purposes, describes a user-interface unit that contains display capability for all possible circuit interrupter options by means of software located solely within the trip unit microprocessor while only displaying those parameters for which the electronic trip unit is configured.
Prior art digital circuit interrupters used within industrial power distribution circuits generally employ a "look-up" table in combination with the trip unit microprocessor to store and display the many trip parameters utilized by the circuit interrupters within a wide variety of industrial power circuit applications. The use of a look-up table to store trip parameters within an electronic trip unit requires correspondingly large memory capacity to store the large number of possible settings for each setpoint. With circuit breakers employing a keypad and display unit such as described within the aforementioned U.S. Pat. No. 4,870,531 it is economically infeasible to utilize expensive memory chips to store the setpoint data.
Accordingly, one purpose of the instant invention is to provide a digital circuit interrupter used within industrial power distribution circuits that is capable of providing a wide variety of trip parameters without requiring a correspondingly large data storage capacity.